This invention relates to a purifying apparatus for removing magnetic material from a fluid, and particularly to a purifying apparatus structure with which it is possible to separate and remove magnetic material from a fluid continuously.
Magnetic separation is a known technology for removing matter from a fluid, and for continuously purifying sea, river or reservoir water or the like. Japanese Unexamined Patent Publication No. S.59-371, for example, discloses a magnetic separator apparatus in which this kind of solid-liquid separation technology is applied, using a high-gradient magnetic filter. As a pretreatment preceding a magnetic separation step, a magnetic powder (such as for example tri-iron tetroxide) and a coagulant (such as aluminum sulfate or aluminum polychloride) are added to the source water to be processed after it is taken in, and the source water is then stirred. When this is done, solid suspended matter and algae, fungi and microorganisms in the source water are bonded with a magnetic floc by the coagulant, forming numerous magnetic coagulations in the form of a colloid, or magnetic material. This magnetic material is then passed through a magnetic separator, to which it is attracted and is thus separated from the source water.
The basic construction of a purifying apparatus using magnetic separation is shown in FIG. 8. It is made up of a conduit 2 having a filter 3 disposed therein, and one end open below the surface of a water reservoir 1. The intake side of a pump 4 is connected to the other end of the conduit 2, and a source water storage tank 5 is connected to the delivery side of the pump 4. A stirring tank 9 connected to the source water storage tank 5 by a pipe 8, has a stirrer 11 driven by a motor 10 mounted thereon. A chemical regulating apparatus 7 is connected to the pipe 8 by a pipe 8A. Magnetic separator apparatus 100 is connected to the stirring tank 9 by the conduit 14 which has a valve 13 disposed therein, while a processed water tank 23 is connected to the magnetic separator apparatus 100 by a conduit 22 via a valve 21. A conduit 24 connects the processed water tank 23 and the reservoir 1.
The apparatus shown in the figure purifies source water from the reservoir 1, and returns it to the reservoir 1 after processing. (The reference numerals in FIG. 8 are the same as in FIG. 1 and FIG. 2.) Source water from the reservoir 1 is pumped by the pump 4 through the conduit 2 and the filter 3 (which removes large pieces of matter), and is temporarily stored in the source water storage tank 5. Magnetic particles of tri-iron tetroxide and a coagulant such as polyaluminum chloride from the chemical regulating apparatus 7 are then added to the source water through the pipe 8A, and it is fed into the stirring tank the stirring tank 9 is stirred by the stirrer 11 rotated by the motor 10. The pretreated water 12, which contains a floc of magnetic material, then passes through the conduit 14 and the valve 13 and flows into a magnetic separator vessel 15.
Electric power is supplied from a d.c. power supply 17 to an air-core coil 16. A magnetic field proportional to the magnitude of the d.c. current is formed inside the cylindrical magnetic separator vessel 15 (which is disposed with its axis vertical), and is evened by porous magnetic poles 18, which are circular plates provided with holes for water to pass through. The air-core coil 16 is surrounded by an iron yoke 19, which-serves as a path for magnetic force lines, to prevent leakage thereof.
Magnetic fine wire packing of a magnetic filter matrix (hereinafter called the matrix) of a high-gradient magnetic filter 20 is magnetized by the above-mentioned evened magnetic field. The magnetic field inside the magnetic separator vessel 15 is disturbed by the magnetized magnetic fine wire packing, so that concentrations of magnetic flux occur locally, creating many parts having high magnetic field gradients. Thus, when the pretreated water 12 containing the magnetic floc is fed upward, the magnetic floc is caught on the surface of the magnetic fine wire of the packing by a large magnetic force. Purified source water therefore passes as processed water through the valve 21 and the conduit 22 and is temporarily stored in the processed water tank 23 before being returned to the reservoir 1 through the conduit 24.
When a predetermined amount of magnetic floc has been caught on the high-gradient magnetic filter 20, it must be backwashed to restore its magnetic separation performance. First the valve 13 is closed, so that feeding of the pretreated water 12 is stopped, and the d.c. power supply is cut, eliminating the magnetic field. A predetermined amount of processed water is then passed back from above the high-gradient magnetic filter 20 through the valve 21 and a valve 25 is opened. At the same time, air is supplied from an air tank 26 through a valve 27 and a pipe 28 and air-bubbling is carried out. In this manner, magnetic floc adhering to the surface of the magnetic fine wire is washed off, and the washing water is stored in the backwash water tank 29. This washing water is separately taken from the backwash water tank 29 and is finally disposed of, either by discarding it in a landfill or by drying and burning it.
After backwashing, the valves 25 and 27 are closed, a d.c. current from the d.c. power supply 17 is once again supplied to the air-core coil 16, the valve 27 is opened, and magnetic separation is resumed.
One disadvantage of this type of purifying arrangement is that during washing of the high-gradient magnetic filter 20 it is necessary to stop purification operation, which decreases the amount of water that the apparatus can purify and reduces the purification operation efficiency
Japanese Unexamined Patent Publication No. S.59-371 discloses a method which permits continuous purification by providing two magnetic separation parts which are operated and backwashed alternately. However, this arrangement requires electromagnets in each of the magnetic separation parts, so that the manufacturing cost and installation space are greater.
Japanese Unexamined Patent Publication No. S.61-118112 discloses another arrangement which permits purification to be carried out continuously. A magnetic filter matrix disposed in the magnetic field is divided into a plurality of stages in the fluid flow direction and each stage is movable in a direction perpendicular to the fluid flow direction so that their directions of movement are opposite. A magnetic filter matrix is moved to outside the magnetic field, washed and then moved back into the magnetic field. However, in this publication, there is no mention of the relationship between the magnetic flux direction inside the magnetic field and the fluid flow direction, of the details of the structure of the magnetic filters (magnetic filter matrixes) moved in and out of the magnetic field, or of a method for preventing leakage of washing water into the magnetic field. Also, with this apparatus, because the ends of the magnetic filters move as far as the boundary between the inside and the outside of the magnetic field, there is the problem that a large magnetic force acts on the filter in one direction; consequently a large driving force is required to move the filter. Furthermore there is the problem that some washing water containing magnetic floc detached by backwashing flows back through the filter into the magnetic field space and leaks to the magnetic field side and into the purified water.